Author Topic: 71 CB750 Rear Bearing Failure - PICS (Read 3218 times)

thomasd · « **on:** August 05, 2013, 12:44:55 PM »

First post here - thought everyone might be interested to see the damage from 40-year-old wheel bearing failure. Started wobbling on the highway. Right as I pulled off and into the parking lot of the meeting spot for a local club, the drum completely separated from the hub. Lucky it happened at 5mph instead of 70. You'll see in the photos that the inner race is resting on the spacer and all the balls were free in the drum. Absolutely no rubber left.

Anyone got a 16" wheel to sell?

thomasd · « **Reply #1 on:** August 05, 2013, 12:46:24 PM »

Couple more photos. Lesson learned: when buying a vintage bike, always take the wheels apart and swap the bearings/check the shoes. Even if everything else on the bike is brand new!

70CB750 · « **Reply #2 on:** August 05, 2013, 12:55:59 PM »

Nice!

Glad you are ok!

You can post on the wanted board, I am sure somebody has what you need:

http://forums.sohc4.net/index.php?board=45.0

Johnie · « **Reply #3 on:** August 05, 2013, 12:57:01 PM »

OUCH....nice pics. Glad you were low speed. I like your advise and have already changed out the bearings on 3 of the 750's. The K3 had 5,300 miles on it when I found it inside a clean garage. Have not done those yet but should. Good advise...and be sure to go with sealed bearings now.

Kevin D · « **Reply #4 on:** August 05, 2013, 01:31:59 PM »

Yipes! glad you're OK and managed to ride it out.
Whats up with that brake shoe? The friction material is gone?
The brake shoe was keeping the wheel centered?

My old wheel bearings were OK after 40 years and 60000 miles but when I considered the grease was also 40 years old, I changed them out.

Maybe the picture should go to the damage gallery.

thomasd · « **Reply #5 on:** August 05, 2013, 02:15:26 PM »

Quote from: Kevin D on August 05, 2013, 01:31:59 PM

Yipes! glad you're OK and managed to ride it out.
Whats up with that brake shoe? The friction material is gone?
The brake shoe was keeping the wheel centered?

My old wheel bearings were OK after 40 years and 60000 miles but when I considered the grease was also 40 years old, I changed them out.

Maybe the picture should go to the damage gallery.

The rear brake hasn't functioned since I bought the bike at the beginning of the summer. That should have been my clue to take the wheel off. I assumed it was a spring issue because you could not hear metal on metal. I see now that they were probably just worn down from day one. Yes, I think the brake was keeping the wheel centered, but as soon as the lip broke from friction and heat, the whole wheel came completely loose.

Wasn't aware of the damage or wanted threads. Thanks!

Black 750K8 · « **Reply #6 on:** August 05, 2013, 04:35:47 PM »

I know it is to late now but. With a new to you bike take both wheels off if for no other reason check the brakes. Now go to the front and check the hydraulics.

Bootlegger56 · « **Reply #7 on:** August 05, 2013, 05:37:12 PM »

Another good reason to center stand the bike and check swing arm and bearings. I do mine every chain lube. It may not be rocket science but I spin and listen and grab, pull and tug. When I was young I didn't worry about riding or driving fast. Now that I am a dirty old man I keep thinking about wheel bearings or other components failing when I twist things up. I don't rejuvenate as fast as I used too!!!!

thomasd · « **Reply #8 on:** August 07, 2013, 01:21:39 AM »

Thanks for the advice. Yes, I'll definitely be changing the front bearings and looking for any other issues. I'm in my early twenties and don't have as much experience as some of the other members around here, so your advice is much appreciated. Thanks again!

Johnie · « **Reply #9 on:** August 07, 2013, 06:02:29 AM »

There are a ton of posts about changing out those bearings. 3 in the back and 2 in the front. Do a search and you will find them with pics. Let us know how you come out. Oh, welcome to the forum...

CycleRanger · « **Reply #10 on:** August 07, 2013, 06:57:20 AM »

Quote from: thomasd on August 05, 2013, 12:46:24 PM

Couple more photos. Lesson learned: when buying a vintage bike, always take the wheels apart and swap the bearings/check the shoes. Even if everything else on the bike is brand new!

So much THIS!

Practically the first thing I do for any vintage bike is pop in new bearings, no matter what the mileage.

Johnie · « **Reply #11 on:** August 09, 2013, 03:47:27 PM »

Good advise on the bearings for sure. Got me off my keyster to start on the K3 bearings today. Like I said above the mileage was only 5,300 when I got the bike so I let it slide and worked on more pressing issues. Today got the front changed out and had a great test ride. Next bad weather day I do the 3 back bearings. I was surprised at how good they looked for being 40 years old. Nice to have all sealed bearings now.

PeWe · « **Reply #12 on:** August 10, 2013, 10:26:51 PM »

A correctly mounted and lubed bearing will last for very long time. I have however, old extra rear hubs without the rubber seal on the brake side that might be something that cause eaflier failures.

Johnie · « **Reply #13 on:** August 11, 2013, 07:51:06 PM »

Like I mentioned above, waiting for a rainy day to do the 3 back bearings in the K3...today was the day. Everything fell into place and got to dig into the Hondaman book for some excellent tips.

Tews19 · « **Reply #14 on:** August 11, 2013, 09:46:21 PM »

Quote from: Johnie on August 11, 2013, 07:51:06 PM

Like I mentioned above, waiting for a rainy day to do the 3 back bearings in the K3...today was the day. Everything fell into place and got to dig into the Hondaman book for some excellent tips.

SHOW OFF!

Looks great. I forget but what lift did you go with?

Johnie · « **Reply #15 on:** August 12, 2013, 06:10:15 AM »

Thanks Nick....I went with the Handy lift and added both side platforms.

MCRider · « **Reply #16 on:** August 12, 2013, 06:45:36 AM »

Quote from: CycleRanger on August 07, 2013, 06:57:20 AM

Quote from: thomasd on August 05, 2013, 12:46:24 PM
Couple more photos. Lesson learned: when buying a vintage bike, always take the wheels apart and swap the bearings/check the shoes. Even if everything else on the bike is brand new!

So much THIS!

Practically the first thing I do for any vintage bike is pop in new bearings, no matter what the mileage.

Yes, this goes to a point I am want to make. At this point, low mileage on a CB750 is not necessarily a good thing. Even a 78 is 35 years old. There is insidious damage that time alone deals out.

The OEM bearings are only sealed on one side. The inside is open to the hub. So, through condensation cycles, the grease can be polluted by water and hence the bearings too. Then rust. Then everything comes apart.

Same for all the rubber bits, carbs, carb boots, gas tank interior, tires and tubes, cables, etc. All may look good from low mileage, even indoor storage. But they could be useless from age.

And the sheathing on electrical wiring gets brittle and cracks open.

15 years ago, a low mileage 78 or earlier may still have low mileage value. Now, not so much.

MCRider · « **Reply #17 on:** August 12, 2013, 06:58:41 AM »

I'm a little suspicious that in this case there may be a piece missing. Since it was converted to a 16", someone has been in there before.

Was the step spacer on the sprocket side, between the carrier bearing and the hub bearing, present?

Johnie · « **Reply #18 on:** August 12, 2013, 01:03:13 PM »

I respect your opinion roto, but bearings will wear out from use no matter how much you grease them. Same way the internals of the motor will not last forever and ever to eternity just by changing the oil and filter often. To think they will last forever...I guess for the $50 I paid for the front and back bearings I have great piece of mind when I am traveling on the highway. Good discussion topic for sure.

Stev-o · « **Reply #19 on:** August 12, 2013, 07:16:43 PM »

I agree with Johnie and MC. I'm rebuilding a wheel right now (new rim and spokes) and new bearings are going in too. It's a no brainer.

CrankyOldGuy · « **Reply #20 on:** August 13, 2013, 05:26:23 PM »

While we are talking about replacements ... has anybody had to replace the rubber dampers in the rear axle drive assembly or should they be replaced simply because of age (+40 years)?

Harry O.

Johnie · « **Reply #21 on:** August 13, 2013, 06:34:40 PM »

Never replaced mine...still bouncy and soft. I have heard of guys replacing them when they get real hard and no longer provide the cushioning.

CrankyOldGuy · « **Reply #22 on:** August 13, 2013, 07:35:23 PM »

Thanks Johnie.

Harry O.

CycleRanger · « **Reply #23 on:** August 14, 2013, 01:57:07 PM »

Quote from: CrankyOldGuy on August 13, 2013, 05:26:23 PM

While we are talking about replacements ... has anybody had to replace the rubber dampers in the rear axle drive assembly or should they be replaced simply because of age (+40 years)?

Harry O.

I replaced them in my K5. The originals were rock hard.

Tugboat · « **Reply #24 on:** August 14, 2013, 03:32:43 PM »

This bike is currently in my garage (Hi @thomasd!) waiting for a new wheel. Yes - all the spacers were there, including the stepped spacer that goes between the hub and the sprocket carrier. Hopefully you'll be back on the road soon!

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Author Topic: 71 CB750 Rear Bearing Failure - PICS (Read 3218 times)

Black 750K8